1. Field of the Invention
The present invention relates generally to a power train supporting apparatus in the engine compartment of a vehicle more particularly, the presesent invent ion relates to a power train supporting apparatus that can moderate the impact load applied to the passenger compartment when the vehicle bumps against an obstacle.
2. Description of the Related Art
Recently, the merits of small size vehicles have been evaluated from the standpoint of energy consumption and environmental costs. In reducing the size of a vehicle, it is necessary to ensure passenger comfort. Accordingly, small size vehicles are designed such that the limited body dimensions thereof are efficiently used. Meanwhile, it is important to moderate the impact load applied to the passenger compartment when the vehicle is bumped against an obstacle. Medium size vehicles and large size vehicles have relatively great body dimensions, so it is comparatively easy to take measures for moderating impact loads from collisions. On the other hand, the size of the small vehicles makes it difficult to take such measures. Therefore, there is a need to moderate collision impact loads in small size vehicles.
However, passenger comfort and demand for moderation of impact loads tend to run counter to each other, and it is not easy to satisfy both of these requirements. Generally, in a passenger car, a monocoque frame structure in which frames and body panels are integrated into one unit is employed. In this structure, the engine compartment in which a power train is to be housed is surrounded by side members, a front cross member, a toe board, etc. The power train is supported on the side members via mounts.
Provided that a vehicle having an engine located at its front bumped head on against an obstacle, the side members, which are located frontward of the passenger compartment, are subjected to an impact load in their axial directions such that they are likely to undergo compressive deformation. The power train supported on these members may be shifted by this deformation toward the passenger compartment. The impact load is reduced when the energy of the collision is converted into the energy required to deform the side members. A partition located between the engine compartment and the passenger compartment is liable to be damaged by the shifting of the power train during the collision. The degree of such damage to the partition depends on how much energy the side members can absorb before the power train is shifted. In other words, it depends on how much allowance for contraction the side members each have.
Since medium and large size vehicles generally have relatively long lengths, sufficient allowance for contraction is available in the side members. Accordingly, it is possible in medium and large size vehicles to provide necessary dimensions for the passenger compartment as well as to moderate impact loads. Damage to the partition of the passenger compartment caused by shifting of the power train can be controlled by the allowance for contraction in the side members. On the other hand, in small vehicles, it is not easy to simultaneously provide sufficient dimensions for the passenger compartment and a sufficient allowance for contraction for the front side members so as to control damage to the partition caused by shifting of the power train at collision.
German Laid-Open Patent Publication No. DE4326396A1 discloses an arrangement for an automotive prime mover (power train) in a vehicle having an extremely short bonnet, which can prevent the partition of the passenger compartment from being damaged by shifting of the prime mover (power train) at collision. As shown in FIG. 9, in a vehicle, a front mount 102 and a rear mount 103 support a prime mover 101 such that it is tilted forward below a toe board 100. The toe board 100 has a slant face 104 having substantially the same slant angle as that of the prime mover 101.
When the vehicle bumps against an obstacle, the front mount 102 releases the connection with the prime mover 101. The thus released prime mover 101 is guided along the slant face 104 of the toe board 100 toward the space under a floor panel 105. Thus, damage of the partition (including the toe board 100) caused by shifting of the prime mover 101 can be prevented.
FIGS. 10 and 11 each show a structure for moderating the collision impact upon a steering wheel in the passenger compartment. In a first impact moderating structure shown in FIG. 10, two steering shafts 110, 111 are connected to each other by a joint 112. According to this structure, the joint 112 separates at collision when the wheel 113 drops to release the connection between the shafts 110 and 111. Thus, the impact load acting upon the wheel 113 is moderated.
In a second impact moderating structure shown in FIG. 11, a steering wheel 120 is connected to a steering gear box 124 via a corrugated tube 121, a ball joint 122, a steering shaft 123 and another ball joint 122. According to this structure, the tube 121 is bent at collision to pivot the shaft 123 upward. Thus, the distance between the gear box 124 and the wheel 120 is shortened to moderate the impact load applied to the wheel 120.
However, in the prime mover (power train) arrangement structure described above, the prime mover 101 must be located below the toe board 100, and thus there is little design freedom in arranging the prime mover 101. Accordingly, in employing this arrangement in a vehicle, a special design must be contrived so that the prime mover 101 is located below the toe board 100. Further, in order to locate the prime mover 101 at a lower position, special designs must be contrived for the engine compartment and the suspension. Accordingly, a conventional power train and framework cannot be used. In other words, such an arrangement cannot be applied as such to existing vehicles. Therefore, there is a need for a structure that can moderate the impact load acting upon the passenger compartment based on minimal changes and improvements in the structure of existing small vehicles.
Meanwhile, in the arrangement shown in FIG. 9, this structure may fail to work properly in case of an offset collision, where one side at the front face of the vehicle bumps against an obstacle. That is, there is a fear that the prime mover 101 will not be guided smoothly to the space under the floor panel 105.
In the first impact moderating structure shown in FIG. 10, it is difficult to set the load for separating the joint 112 at an appropriate value relative to the impact load. More specifically, when the vehicle bumps lightly against an obstacle, rides over a hump or a gap, or when the vehicle runs on irregular ground, the joint 112 is not permitted to separate. The joint 112 is expected to separate only when the vehicle bumps heavily against an obstacle.
In the second impact moderating structure shown in FIG. 11, the rigidity of steering is lowered if the length of the corrugated tube 121 is increased very much. Accordingly, in order to maintain steering rigidity, a sufficient distance for contraction cannot be provided between the gear box 124 and the wheel 120. These two contradictory factors limit the design.